An investigation into the Optus triple zero outage has revealed it can take up to a minute for an emergency call to be re-routed over another telco’s network under a process called ‘camp-on’.
The issue impacts both Apple and Samsung devices, according to Optus.
Camp-on is a regulated process intended to ensure triple zero calls are carried over any available network in the vicinity of the user’s handset, particularly if their own provider’s mobile service can’t carry the call.
There is a suspicion that the heavy delay in having an emergency call re-routed to healthy network infrastructure is unknown and intolerable for callers, causing them to hang up before the re-routing process is complete.
“What emerged from the behaviour of devices … is that for many calls it may take 40-60 seconds to camp-on,” the Dr Kerry Schott review [pdf] into Optus’ September triple zero outage found.
“In an emergency, people are unlikely to hang on for this length of time, especially when the only response they are getting is silence on the line.
“Emergency calls that take 40-60 seconds to connect are not ideal and the community must be made aware of the issue.
Schott added: “This is a technical matter that the industry and government must investigate further – and as soon as possible.”
The finding is likely to put more pressure on the government to revamp the triple zero system.
Schott suggested aspects of the system may be outdated.
“The triple zero system was designed in the days of 2G and 3G. It is possible that standards and regulations – and the system as a whole – have not kept up with the changes in the network since then and the greater sophistication of devices,” he wrote.
“Devices have different characteristics, and each connects with the network settings of different carriers.
“The triple zero system is based on voice calls at present, even though many emergency services are using data services extensively. It may be worth exploring whether triple zero should also allow data services.”
Slow camp-on
The Schott review states that when the primary voice gateway a customer uses is unable to carry an emergency call, their device “chooses some other option” – a decision “influenced by the characteristics of different mobile devices, timing settings in the network, and how these factors interact.”
At the time of Optus’ September outage, its network had a different setting to others, which controlled “how long an emergency call remains actively attempting to connect.”
Where other networks had a time-out setting of 150 to 600 seconds, Optus had set its time-out to 10 seconds. It was designed to address an issue experienced by Google Pixel 6A users.
“Optus reduced their emergency inactivity timer to 10 seconds to enable faster retries after call failures,” the review stated.
The telco has since reverted to 600 seconds.
Lab tests where the 10-second time-out setting was enabled showed that the different call pathways that Apple and Samsung devices used to try to get an emergency call to go through.
Both had issues with 40-60 second connection times in some circumstances.